In a process of network development towards broadbandization and mobilization, the 3rd Generation Partnership Project (3rd Generation Partnership Program, 3GPP) organization puts forward a Long Term Evolution (Long Term Evolution, LTE) scheme, that is, an evolved universal terrestrial radio access network (E-UTRAN), for a mobile access network; and a system architecture evolution (SAE) scheme, that is, an evolved packet core (Evolved Packet Core, EPC), for a mobile core network.
An E-UTRAN adopts a single-layer structure consisting of only an evolved NodeB (eNB) to simplify a network and reduce a delay. An interface between a user equipment (UE) and an eNB is a Uu interface, which is a radio interface. A user plane of a Uu interface is mainly used to transfer an Internet Protocol (IP) data packet, and mainly completes functions such as header compression, encryption, scheduling, a hybrid automatic repeat request (HARQ), and an automatic repeat-request (ARQ). A signaling plane of a Uu interface is mainly used to transmit a signaling message. Control plane signaling of a UE, for example, radio resource control (RRC) signaling, is mapped to a signaling radio bearer (SRB) for transmission; and all IP data packets of a user plane are mapped to different data radio bearers (DRB) for transmission. An SRB and a DRB are first processed by a packet data convergence protocol (PDCP) sublayer and a radio link control (Radio Link Control, RLC) sublayer respectively, and then are multiplexed at a media access control (Media Access Control, MAC) sublayer. A DRB and an SRB of a UE share a same MAC entity, that is, a user plane and a control plane of a same UE are anchored on a same eNB.
In a case that overlapped coverage exists between a macro cell and a micro cell, for a UE with high mobility, if the UE is attached to a macro eNB with a large coverage scope, factors affecting user experience, such as a service interruption and throughput reduction that may be caused by frequent handovers, can be avoided. However, the UE needs to be connected to a macro eNB that is relatively far away, which requires an increase in transmit power and air interface resource consumption. If the UE is attached to a near pico eNB, air interface resource consumption can be reduced but the number of handovers and a handover failure ratio may be increased, thereby causing a service interruption of the UE.
For the foregoing problem, an idea of separating an air interface control plane from a user plane is put forward in the prior art, where a signaling base station (signalling BS) provides a signaling connection for a UE and a data base station (Data BS) provides a data connection for the UE. However, an access problem of the UE is not solved.